The present invention relates generally to microelectromechanical system (MEMS) devices and, more particularly, to MEMS magnetically actuated switches and associated switching arrays.
Microelectromechanical systems (MEMS) have recently been developed as alternatives for conventional electromechanical devices such as relays, actuators, valves and sensors. MEMS devices are potentially low cost devices, due to the use of simplified microelectronic fabrication techniques. New functionality may also be provided because MEMS devices can be physically much smaller than conventional electromechanical devices.
Many potential applications of MEMS technology utilize MEMS acuators. For example, many sensors, valves and positioners use actuators for movement. If properly designed, MEMS actuators can produce useful forces and displacement, while consuming reasonable amounts of power. MEMS actuators, in the form of microcantilevers, have been used to apply rotational mechanical force to rotate micromachined springs and gears. Piezoelectric forces have also been employed to controllably move micromachined structures. Additionally, controlled thermal expansion of actuators or other MEMS components has been used to create forces for driving microdevices. One such thermal actuator is disclosed in U.S. Pat. No. 5,475,318 entitled xe2x80x9cMicroprobexe2x80x9d issued Dec. 12, 1995 in the name of inventors Marcus et.al., which describes leveraging thermal expansion to move microdevices.
Micromachined MEMS electrostatic devices have been created which use electrostatic forces to operate electrical switches and relays. Various MEMS relays and switches have been developed which use relatively rigid cantilever members, or flexible flaps separated from the underlying substrate in order to make and break electrical connections. Examples of such rigid cantilever MEMS electrostatic devices are disclosed in U.S. Pat. No. 5,367,136, entitled xe2x80x9cNon-Contact Two Position Microelectronic Cantilever Switchxe2x80x9d, issued Nov. 22, 1994, in the name of inventor Buck and U.S. Pat. No. 5,544,001, entitled xe2x80x9cElectrostatic Relayxe2x80x9d, issued Aug. 6, 1996, in the name of inventors Ichiya et. al. Additionally, an example of an electrostatic MEMS switch embodying a flexible type flap arrangement is disclosed in U.S. patent application No. 09/345,722, entitled xe2x80x9cHigh Voltage Micromachined Electrostatic Switchxe2x80x9d filed on Jun. 30, 1999, in the name of inventor Goodwin-Johansson, and assigned to the same entity as the invention herein disclosed.
While magnetic fields, and more specifically electromagnetic fields, have also been used to drive micromotors and to activate switches, typically previous use of magnetic fields has dictated that each micromotor or switch have an individual magnetic field associated with it. For example, conventional MEMS switching matrix have included individual microcoils or electromagnets to drive each individual switch element in the array, thereby resulting in an undesirably large and complex switch. The size and complexity of the switch are particularly troublesome, as the switching matrix becomes large, as demanded by some applications. In addition, most conventional switching matrices are limited to in-plane operation. As such, the need exists to create MEMS magnetically actuated switches that can be actuated in an in-plane or out-of-plane direction to accommodate switches capable of directing current from and to electrical load lines disposed on a single microelectronic substrate and from and to electrical load lines disposed on two distinct microelectronic substrates.
As such, a need exists to provide MEMS magnetically actuated switches and corresponding switching arrays that are capable of individual activation in a single magnetic field environment. This benefit can be realized in easier fabrication of large scale switching arrays that occupy less space on the microelectronic substrate. These benefits are particularly attractive since switching devices and the associated arrays are highly desirable in today""s telecommunications and test equipment industries.
A MEMS magnetically actuated cross point switch and associated switching arrays are therefore provided that are capable of providing in-plane and out-of-plane actuation while occupying minimal area on the microelectronic substrate. Additionally, the MEMS magnetically actuated cross point switch of the present invention provides for a concise array that can be actuated by a single external magnetic field source.
The MEMS electrical cross-point switch includes a microelectronic substrate, a magnetic element attached to the microelectronic substrate that is free to move in a predetermined direction in response to a magnetic field and an electrical element connected to the magnetic element for movement therewith to selectively switch electric current. In operation, the magnetic element is in communication with a magnetic flux path and seeks to align with the magnetic field across the flux path to create the actuation force. The actuation force drives the electrical element to electrically connect with a proximate electrical load path. In one embodiment the magnetic element and the electrical element are connected via a tethering device that acts as a platform for the magnetic and electrical elements. The electrical cross-point switch may also comprise a clamping element that serves to lock the switch in an open or closed position to circumvent the magnetic actuation of the switch.
In another embodiment, the invention provides for a MEMS electrical cross-point switching array that includes a microelectronic substrate, a magnetic field source in circuit with said microelectronic substrate, a plurality of first and second electrical lines disposed on the microelectronic substrate in an array formation, and a plurality of the in-plane MEMS electrical cross-point switches as described above disposed at the cross point of a first and second electrical line. In one embodiment the magnetic elements and the electrical elements of the individual switches are connected via tethering devices that act as platforms for the magnetic and electrical elements. The individual electrical cross-point switches may also comprise clamping elements that serve to lock the switch in an open or closed position to circumvent the magnetic actuation of the switch when the magnetic field source is applied to the array. In one embodiment the array is configured in a Nxc3x97N or Nxc3x97M array having a series of crossing first and second electrical load lines. In another configuration the array has a series of first electrical load lines that extend in circular arcs from a central point of reference and a series of second electrical load lines that extend outward, in a radial spoke-like fashion, from the central point of reference. In both embodiments switch elements are located at the cross point of the intersecting first and second electrical load lines.
In another embodiment the MEMS magnetically actuated cross-point switch includes a microelectronic substrate and a magnetic element attached to the microelectronic substrate and free to move in a predetermined direction in response to a magnetic field to selectively switch electric current from a magnetically conductive first electrical line to a second electrical line. In this embodiment the electrical load path and the magnetic flux path are shared, such that magnetic actuation of the magnetic element results in the select switching of electric current from one electrical load line to another. In this embodiment, a clamping element may be employed to lock the switch in an open or closed position to circumvent the magnetic actuation of the switch. In another embodiment a corresponding MEMS magnetically actuated switching array is provided that includes the MEMS switches described above.
In yet another embodiment, an out-of-plane MEMS magnetically actuated cross-point switch includes a first microelectronic substrate and a first contact plate disposed on the first microelectronic substrate that is magnetically moveable. This switch also comprises a second microelectronic substrate positioned in a spaced apart relationship with the first microelectronic substrate. The second microelectronic substrate has disposed thereon a second contact plate located proximate to the first contact plate, wherein the selective magnetic actuation of the first contact plate results in the switching of electrical current from the first contact plate to the second contact plate. In this dual substrate embodiment the second contact plate on the second substrate may be capable of magnetic actuation or the second contact plate may be a stationary entity. In this embodiment, a clamping element may be employed to lock the first contact plate in an open or closed position to circumvent the magnetic actuation of the switch. In an alternate embodiment an array of the above described switches can be formed on the first and second substrates to selectively change current from a series of first electrical load lines on the first substrate to a series of second electrical load lines disposed on the second electrical substrate.
Additionally, a method for MEMS electrical switching is provided that includes the steps of applying a magnetic field to a magnetically actuated MEMS electrical cross-point switch, attracting a magnetic element of the switch toward the magnetic field, actuating an electrical element connected to the magnetic element and switching electric current. Additionally, the method may provide for clamping the switch prior to application of the magnetic field to lock the switch in an open or closed state.
As such, the present invention provides for a MEMS magnetically actuated switch and corresponding switching arrays that are capable of individual activation in a single magnetic field environment. This benefit is realized in easier fabrication of large scale switching arrays that occupy less space on the microelectronic substrate.